Patent GB-817959-A (GB)
Title: Switching systems applicable particularly to group selection in automatic telephony systems
IPC: H04Q3/00
Filed: 1956-02-03
Abstract: 817,959. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. Feb. 3, 1956 [Feb. 4, 1955], No. 3466/56. Class 40 (4). In group selection equipment, identical units are employed each consisting of a number of cross-bar switches constituting a primary stage and a number of cross-bar switches constituting a secondary stage with links between the stages such that each inlet of the primary stage has access through at least one link to each outlet of the secondary stage. Each unit has n inlets and p outlets and an equipment having B A inlets and B outlets is provided bysubp A groups each of - units (the values of A, B, n A B n,p, - and - all being positive integers), each n p of the A inlets being multipled to a single corresponding unit in each sub-group, and each of the B outlets being multipled to every unit of a single respective sub-group, each of the A inlets having access to every one of the B outlets. In the embodiment described (Fig. 1) each unit has 400 switch inlets and 400 switch outlets. These are not multipled within the unit, so each unit has 400 unit inlets and 400 unit outlets. A sub-group, such as EG1, comprises two units SG11, SG12, only one primary switch (GSP11), one secondary switch (GSS11) and one link (JI11) being shown in each unit. Eight hundred incoming junctions JE1, JE2 are multipled to the two sub-groups EG1, EG2, each of which sub-groups serves 400 outgoing junctions (JS1, JS2, respectively). Operation.-When an incoming junction calls the condition is recognized by the connecting circuit, such as CCE1, whereupon the test circuit T of the register-finder CE detects the calling junction, hunts for a free register E, and causes the register-finder to connect the junction to the register. The register then receives the identity of the calling junction from the test circuit T and that of the wanted direction from the incoming junction, both of which identities it transfers to one of the receivers R. Those directions to which free outgoing junctions exist are indicated by the device D which consists of a field of terminals one per direction per subgroup. A characteristic potential is applied to each terminal when there is in the corresponding sub-group at least one free junction in the relevant direction, and each receiver R has access to these terminals via a group of connecting wires FC5. As the equipment described consists of two sub-groups and as only two directions will be considered, the field of terminals (Fig. 2) has four terminals d11 and d12 for direction DR1, and d21 and d22 for direction DR2. The receiver now causes the closure of contacts such as FC511 and FC512 corresponding to the wanted direction and receives, by virtue of the potential applied to RT1 or RT2 or both, an indication of those sub-group(s) capable of completing the connection. If there is more than one, it selects one, say EG1, and is then connected to a free marker, say MG11, associated with that sub-group to which it transmits the identity of the incoming junction and that of the required direction. The marker is thereupon connected to the set of connecting relays RC11 of the unit SG11 to which the incoming junction is wired, and controls the setting up of the desired connection. Modificationsto meet differing traffic conditions.-By multipling the switch inlets two by two and multipling the switch outlets two by two, group selection units are obtained each of which has 200 unit inlets and 200 unit outlets, each unit inlet having access to each unit outlet through four links. The traffic carrying capacity is thus increased since if a bar serving one cross point is in use, three alternatives are available over which the desired connection may be established. Each sub-group which is to receive 800 incoming junctions will consist of four units, and in order to deal with the 800 outgoing junctions four sub-groups such as EG1 (Fig. 1) will be required. If then it is required to double the number of incoming and outgoing junctions (to 1600 of each), this may be done in one of several ways depending upon the density of traffic. Firstly the switch inlet multiple of each unit may be suppressed so that each unit again has 400 unit inlets, eight sub-groups being required to provide 1600 unit outlets, and each unit inlet having access to each unit outlet through two links. Secondly, the switch outlet multiple may be suppressed so that each subgroup has 400 outlets. The number of units in a sub-group is increased to eight and the number of sub-groups remains at four, each unit inlet again having access to each unit outlet through two links. Thirdly, both the switch inlet and switch outlet multiples of each unit may be suppressed so that each sub-group has 1600 inlets for the 1600 incoming junctions and 400 outlets for 400 outgoing junctions. Neither the number of units per sub-group nor the number of subgroups is altered, each unit inlet having access to each unit outlet through one link only. Fourthly, the multiples need not be suppressed, but the number of units per sub-group and the number of sub-groups may be doubled, each unit inlet then having access to each unit outlet through four links..